1. Field of the Invention
The present invention relates to the field of image sensors, usable for example in video cameras.
2. Discussion of the Related Art
Among the various techniques for converting an image projected on a target into electric data, targets formed of a semiconductor substrate supporting an array of photodiodes are used. The diodes are generally reverse-biased and capacitively charged. In the absence of light, they keep their charge and, when lit, they discharge. A bright image element or pixel can thus be differentiated from a dark pixel and an image in the form of a matrix of data corresponding to the electric charges of each of the pixels can thus be restored.
Further, it is known to form this matrix so that all pixels are divided into three sub-arrays corresponding to each of three colors (currently, red, green, and blue). For this purpose, each of the pixels, that is, each of the diodes, is coated with a color filter. It is known to use an interference filter as a color filter. Interference filters formed of materials compatible with usual MOS-type integrated circuit manufacturing lines have also been provided. Thus, an interference filter may be formed of a silicon oxide layer coated with a polysilicon layer, itself coated with a silicon nitride layer. In fact, the successive materials have to alternately have low and high optical indexes.
In such structures, the storage capacity of each pixel is associated with the pixel dimension and more specifically with the dimension of the junction of the associated diode.